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2013.03.14 学会予聴会
2013.03.07 "TBA" Abdel Jawad Majed
2013.02.28 文献調査
2013.02.21 平成24年度研究報告3 山下 穣、圓谷 貴夫、Abdel Jawad Majed
2013.02.14 平成24年度研究報告2 崔 亨波、大滝 大樹、上田 康平
2013.02.07 平成24年度研究報告1 大島 勇吾、田久保 直子、梶田 初葉
2013.01.31 "Photo-Induced Insulator-to-Metal Transition in Charge-Ordered BEDT-TTF Salts" 田久保 直子
I would like to present my work at the CMM group. I have investigated photo-induced insulator-to-metal transition (PIMT) in charge-ordered (CO) BEDT-TTF salts focusing on how photo-induced state is like and what material condition showing PIMT is.
First of all, I developed simultaneous optical and transport measurement system. I observed photo-induced state in α-(BEDT-TTF)2I3 thin crystal using the simultaneous measurement system. It was suggested that the photo-induced state is macroscopic metastable metallic phase and inhomogeneously grows.
Second, I investigated photo-induced effects in two CO BEDT-TTF salts; (BEDT-TTF)3X2 (X = ReO4, ClO4). PIMT was observed in a ReO4 salt where the CO state is associated with a lattice distortion. On the other hand, no PIMT was noted in a ClO4 salt where the CO state is not accompanied by distinguishable structure change. This comparative study suggested that the lattice distortion plays a key role in the stabilization of the photo-induced phase.
2013.01.24 "Vibrational Spectra of X[M(dmit)2]2 and a Diversity in the Ground State of X[Pd(dmit)2]2" 山本 貴博士（大阪大学大学院理学研究科化学専攻物性物理化学研究室（中澤研究室））
Vibrational spectroscopy is useful to analyze not only the molecular structure but also the inter-molecular interaction.
In this seminar, some useful vibrational modes of X[M(dmit)2]2 will be introduced. On the basis of the experimental results for X[Pd(dmit)2]2, the relationship between the ground states and the inter-molecular interactions will be discussed.
2013.01.17 "Spin Structure and Dynamics of Volborthite with a Distorted Kagome Lattice" 吉田 誠博士（東京大学物性研究所滝川研究室）
The possibility of exotic quantum states in two-dimensional spin systems with frustrated interactions has attracted strong attention. Volborthite Cu3V2O7(OH)2*2H2O, which has distorted kagome layers, is an example of interesting frustrated spin systems. The absence of magnetic order down to 2K, much lower than the Curie-Weiss temperature -115 K, indicates strong effects of frustration. Unusual sequential magnetization steps at 4.3, 26, and 46 T were reported. We have performed 51V-NMR experiments on the powder and single-crystal samples of volborthite. Three distinct magnetic phases were found at low temperature phase-I below 4.5 T, II up to 26 T, and III above, consistent with the magnetization results. Phase I shows anomalies such as a Lorentzian line shape, a 1/T1 \propto T behavior indicating dense low-energy excitations, and a large spin-echo decay rate 1/T2 pointing to unusually slow fluctuations. Both phases II and III exhibit a heterogeneous spin state consisting of two spatially alternating Cu spin systems, one of which exhibits anomalous spin fluctuations contrasting with the other showing a conventional static order. The magnetization of the latter system exhibits a sudden increase upon entering into phase III, resulting in the second magnetization step at 26 T. We discuss the possible spin structure with particular reference to the theories on the anisotropic kagome lattice.
2012.12.27 文献調査
2012.12.20 "Chemistry and Physics in κ-H3(Cat-EDT-TTF)2 ~from purely organic single-component conductor to quantum spin liquid~" 磯野 貴之博士（東京大学物性研究所森研究室）
An organic dimer-Mott system, κ-H3(Cat-EDT-TTF)2, synthesized by us recently, provides attractive research topics in both chemical and physical standpoints. In the seminar, I will talk about the three topics, as follows;
1) Hydrogen bond-promoted metallic state in a purely organic single-component conductor
Purely organic materials are usually insulating. To provide electrical conductivity for them, some charge-carrier generation is needed. In purely organic single-component systems, however, metallic states have rarely been realized. Here, we indicate that `symmetric' hydrogen bonding between H2Cat-EDT-TTF molecules forms a new type of purely organic single-component conductors, and realizes high room-temperature conductivity and a low-pressure metallic state.
2) Possible quantum spin liquid in spin-1/2 organic triangular lattice
Conventional spin systems fall into long-range ordering states at sufficiently low temperature. Exceptionally, these states are prevented through quantum fluctuation and spin frustration, and thus quantum spin liquid (QSL) emerges. So far, however, there have existed only a few experimental QSL candidates, e.g. EtMe3Sb[Pd(dmit)2]2. Here, we discuss the possible QSL state in spin-1/2 triangular lattice with one-dimensional anisotropy through the results of the low-temperature magnetic study.
3) Dramatic deuteration effect
2012.12.06 "Fluorination and Platinization of Dimer Mott R4Z[M(dmit)2]2 Salt" 野村 光城
This seminar should be final for me at the CMM group, thus I would like to present all the things that I have done here. Since Prof. Kato has initiatively developed dimer Mott systems based on R4Z[Pd(dmit)2]2 salts so far, I have modified the salts, as a chemist, by a fluorination of the R4Z+ cation and a platinization of the metal-dmit anion.
Pd(dmit)2 salts with (FCH2)Me3Z+ (Z = N, P) cation showed metallic behavior down to ca. 100 K under ambient pressure, whereas the early R4Z[Pd(dmit)2]2 salts were Mott-insulators in all temperature region unless physical pressure was given. Among them, the β-(FCH2)Me3N[Pd(dmit)2]2 salt demonstrated superconductivity at 4.2 kbar (Tc = 7.4 K), although the corresponding non-fluorinated Me4N+ salt required higher pressure than 4.2 kbar for superconductivity. It is concluded that the fluorination of the R4Z+ cation provides anisotropic chemical pressure to a 2D triangular lattice derived from Pd(dmit)2. The chemical pressure originated from the (FCH2)Me3Z+ cation enhances bandwidth to metallize the dimer Mott system, and reduces required physical pressure to show superconductivity.
The replacement of Pd with Pt in the dimer [M(dmit)2]2 salt drastically modified the intradimer transfer integral (tH, tL) to control a dimerization gap (2|tH|, 2|tL|) as well as degree of HOMO-LUMO band overlap. Pt(dmit)2 salts with small cations (Me4P+, Me4As+) were the novel 'multiband' molecular conductors, since the AB-HOMO and B-LUMO bands were overlapped near Fermi level, thanks to reduction of the dimerization gaps. The intradimer transfer integral of [Pt(dmit)2]2 is highly tunable by applying chemical and physical pressure. I emphasize that the dimer [Pt(dmit)2]2 itself is stretchable with the flexible Pt-Pt bond. The dimer stretch may be origin to show a charge-ordered state in high temperature region (> 150 K), because shrunk dimers [Pt(dmit)2]20 and elongated dimers [Pt(dmit)2]22- existed at the CO state with involving a Pt-Pt bond stretch. Although all the Pt(dmit)2 salts prepared in this work were metallic in high temperature region under ambient pressure, applying hydrostatic pressure suppressed the metallic state. Indeed, giving physical pressure strongly shrinks the dimer [Pt(dmit)2]2 to enhance the intradimer transfer integral: thus, pressure-induced Mott-insulating state may appear. It is contrast that the early R4Z[Pd(dmit)2]2 salts are metallized under pressure.
2012.11.15 "Studying the Fermiology with Millimeter Waves" 大島 勇吾
There are several ways to study the Fermiology in molecular conductors. The most well-known techniques are quantum oscillations such as the Shubnikov-de Hass (SdH) or de Haas-van Alphen (dHvA) effects. The next would be the Angle-Dependent MagnetoResistance Oscillation (ADMRO), which was firstly discovered in molecular conductor. Angle-Resolved PhotoEmission Spectroscopy (ARPES) might be the next-generation tool to study the Fermiology.
However, there are other methods to study the Fermi surface, which use millimeter waves and magnetic field. It's relatively new but an 'expiring' technique where nobody is using it anymore in molecular conductors. It's cyclotron resonance (CR) and periodic orbit resonance (POR). I will talk about the basics of these techniques, and tell you what we can learn from it.
2012.11.08 "Ab-Initio Studies for Molecular based Quantum Spin-Liquid Materials" 圓谷 貴夫
Spin-1/2 quasi-2D system with triangular lattice has attracted much attention recently, because a spin liquid like behavior is found in two molecular crystals κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2.
This discoveries has fascinated both experimentalists and theorists.
The spacial anisotropy is evaluated by calculating transfer integrals based on tight-binding model.
Recently, using first-principles density-functional theory calculations method, transfer integrals can be obtained by numerical fitting for the first-principles band structures or constructing maximum localized Wannier functions.
On the other hand, anisotropic triangular lattice with S=1/2 anitiferromagnetic Heisenberg model has been investigated by various theoretical technique such as variational Monte Carlo simulations, spin-wave theory with exact diagonalization and so on.
In this talk, several theoretical or computational works for the two spin-liquid compounds are introduced, and discuss their anisotropy of the triangular lattice in related to the Heisenberg model calculations. Temperature dependence of the structural and electronic properties are also reported.
2012.11.01 "Crystal Growth under Microgravity and under Magnetic Field" 上田 康平
Any efforts have been done to obtain big and good crystals; purity of starting material, purity of solvent, temperature, concentration and so on. However, many experiment methods, for example neutron scattering, are not useable in our field, because molecular conductor crystal is so small. From the view point of Crystal Growth Field, convection should be treated as important factor for crystal growing. This gives the effect to crystal size, growth ratio, morphology, quality and etc.. The community of structural biology has some solution for controlling convection effect by using microgravity or magnetic field.
In this seminar I will talk about microscopic view of crystal growth and introduce crystal growth experiment under microgravity and under magnetic field.
2012.10.25 文献調査
2012.10.18 "Universality of AC conduction in disordered solids" Abdel Jawad Majed
The AC conductivity in a range of different disordered solids is found to have striking similarities. In this seminar, I will introduce you to "the universality of the AC conductivity in disordered solids".
2012.10.11 "Introduction to Monte Carlo Methods" 大滝 大樹
Monte Carlo (MC) methods are well-known and widely used methods in computer simulations of physical, chemical and mathematical systems.
In this talk, I will introduce theoretical foundations of the methods and show how we can obtain physical properties from MC simulations with some examples.
2012.10.04 "Basics and Application of Liquid Crystals" 野村 光城
Liquid crystal (LC) is a state of matter that has properties between those of a conventional liquid and those of a solid crystal. Thus, a LC shows both fluidity and anisotropy. Any LCs are prepared by organic components (eg. rigid core + flexible alkyl chain) because they are basically soft matters. There are mainly four different LC phases based on the shape of organic molecule and self-organized pattern. I will introduce detailed examples of LC materials derived from tetrathiafulvalenes (TTFs), metal dithiolene complexes, fullerenes and others. A practical LC material is now useful for a liquid crystalline display (LCD). Principles and fundamental molecular design for the LCD are presented. LC molecular conductors, which may be printable by the fluidity and self-organizing property on a substrate, are recently developed.
2012.09.13 "Research in RIKEN" Guilhem Aubin、学会予聴会 上田 康平
2012.08.30 文献調査
2012.08.02 平成24年度中間報告3 大島 勇吾、上田 康平、大滝 大樹、木村 弘志
2012.07.26 平成24年度中間報告2 野村 光城、草本 哲郎、須田 理行、崔 亨波
2012.07.19 平成24年度中間報告1 山下 穣、Abdel Jawad Majed、田久保 直子、圓谷 貴夫
2012.07.05 "Universal Conductivity in Two-Dimensional SC-INS Ttransition" 山下 穣
In this talk, after brief introduction of quantum phase transition, I will review about the theoretical prediction of universal conductance at a quantum critical point between a superconductor and an insulator, and show some relevant experiments done in many systems.
2012.06.28 "How to Make Four Contacts on a Small Sample" 崔 亨波
The four-probe transport measurements is the one most conventional technique for investigating physical properties. However, some system are very difficult to be grown to large size of single crystals. To make good contacts on a small sample is required for accurate measurements. In this seminar, I will present my sample mounting knowledge that I learned during these 10 years. The tools, gold wires, paint, and sample mount procedure will be introduced. Some smart techniques used for sample mounting by other groups will also be presented.
2012.06.21 "Mysterious(?) Ground States of lambda-(BETS)2FeCl4" 大島 勇吾
lambda-(BETS)2FeCl4 is a molecular conductor where strong pi-d interaction exist in the system. Due to this fascinating feature, it shows complementary physical properties both in conductivity and magnetism.
For instance, it shows a metallic behavior down to 8K, and becomes an antiferromagnetic insulator at low temperature. Moreover, when the magnetic field is applied parallel to the conducting plane, it becomes superconducting at 17 T.
All physical properties seem to be well-understood, however, its antiferromagnetic ground state is still a mystery (or maybe physicists (including me) are just messing up everything!!).
In my talk, I will review previous studies performed in this compound, and shed a light to what is understood and to what is not well-understood. If time allows, I will also discuss the ground state of this system.
2012.06.14 文献調査
2012.06.07 "Maximally Localized Wannier Functions; Applications for Molecular Crystals" 圓谷 貴夫
Wannier functions was introduced by G. Wannier in 1937, and is obtained by performing unitary transformations from Bloch functions to a set of localized Wanneir functions (WFs).
However, WFs are not unique function, and the phase indeterminacy of Bloch orbitals at every wavevector k is exist.
An important idea of a "maximally localized (ML)" criterion for finding unique set of WFs has been developed by Marzari and Vanderbuilt in 1997.
This made it possible to have the actual implementations of WFs to first-principles calculation method based on density functional theory.
There are many different advantages for calculating physical properties by using MLWFs such as macroscopic polarizations, anomalous hall effect, van der Waals interactions, and utilization as basis for tight-binding calculations.
In this talk, fundamentals and its appellations of MLWFs are presented. Advantages of WFs in research area of molecular solids are also discussed.
2012.05.31 "Hydrogen Bond Forming Effect for Donor Ability of TTF Derivative" 上田 康平
Recently organic conductor with hydrogen-bond has many attracted because it have some possibility to get new functions. As you know hydrogen-bond is very strong inter molecular interaction, so it use for crystal design to make beautiful assemble system. On second thought, this strong interaction comes from large electrical polarize by H-bond connection. And this connection may change electronic state drastically. Taking H-bond as only strong interaction is not enough to understand H-bond effect for electron donor and accepter molecule. In this seminar, I will talk about H-bond interaction how to change the electric donor ability of TTF derivative.
2012.05.17 "Universality and Critical Exponents" Abdel Jawad Majed
My recent work of the phase diagram in EtMe3P[Pd(dmit)2]2 has yielded unique critical exponents. During this seminar, I will introduce Ising universality and explain what those critical exponents represents and why there are so important.
2012.05.10 "Computational Analysis of Intermolecular Interactions in Hydrogen-Bonded Molecular Crystals" 大滝 大樹
Needless to say, properties of molecular crystals cannot be obtained by simple summation of those of isolated molecule. One of the simplest such properties is the molecular electric dipole moment, which is related to dielectric properties in crystal. I have been interested in hydrogen-bonded molecular crystal and studied the effect of intermolecular interactions on dielectric properties in hydrogen-bonded system by using electronic structure calculations and Monte Carlo simulation. In this seminar, I will introduce the computational methods mentioned above and show how intermolecular interactions affect the dielectric properties in hydrogen-bonded crystal with some computational results.
If time allows, I'd like to talk about my future work.
2012.04.26 "Study of Quantum Liquids at Ultra-Low Temperatures" 山下 穣
What is going to happen when you cooled down materials very close to the absolute zero temperature? Naively, it seems boring because everything freezes at T = 0. It was exactly what people expected in 19th century about the fate of electrons in metals as approaching absolute zero temperature. People expected that resistivity would be simply approaching to infinity or zero because electrons or atoms impeding electron’s motion will be frozen. Instead, in 1911, Kamerlingh Onnes discovered a transition to a superconducting phase of mercury at finite Tc, demonstrating the significance of quantum effects at low temperatures. Since then, variety of interesting phenomena has been studied in so-called “quantum liquids” in which one can see explicit effects of quantum mechanics or quantum statics. Examples of quantum liquids are superfluidity of liquid helium, high-Tc superconductivity of cuprates, and quantum spin liquids.
I've been interested in these quantum liquids, and have studied some of them. In this seminar, I will present my past works including,
1. Rotating Superfluid 3He at ISSP
2. Development of SQUID-based position sensor and the application tostudy of supersolid 4He
3. Clarifying gap structures of iron-based superconductors
4. Study of Quantum spin liquids of organic Mott-insulator
If time arrows, I’ll also show my future plan.
2012.04.19 文献調査
2012.04.09 平成24年度年度計画
